U.S. patent application number 14/443434 was filed with the patent office on 2015-11-26 for an absolute position measuring device and a method of performing an absolute position measurement.
The applicant listed for this patent is NEDERLANDSE ORGANISATIE VOOR TOEGEPAST- NATUURWETENSCHAPPELIJK ONDERZOEK TNO. Invention is credited to Michiel Peter Oderwald, Maurits Sebastiaan van der Heiden, Paul Louis Maria Joseph van Neer.
Application Number | 20150338251 14/443434 |
Document ID | / |
Family ID | 47594303 |
Filed Date | 2015-11-26 |
United States Patent
Application |
20150338251 |
Kind Code |
A1 |
van Neer; Paul Louis Maria Joseph ;
et al. |
November 26, 2015 |
AN ABSOLUTE POSITION MEASURING DEVICE AND A METHOD OF PERFORMING AN
ABSOLUTE POSITION MEASUREMENT
Abstract
The invention relates to an absolute position measuring device,
comprising an optical fiber, an optical strain sensor in optical
communication with the optical fiber, and a volume of material
deforming under influence of a magnetic field. The optical strain
sensor is arranged for sensing deformation of the volume of
material. Further, the device is arranged for multi-dimensional
position measurement.
Inventors: |
van Neer; Paul Louis Maria
Joseph; ('s-Gravenhage, NL) ; Oderwald; Michiel
Peter; ('s-Gravenhage, NL) ; van der Heiden; Maurits
Sebastiaan; ('s-Gravenhage, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NEDERLANDSE ORGANISATIE VOOR TOEGEPAST- NATUURWETENSCHAPPELIJK
ONDERZOEK TNO |
's-Gravenhage |
|
NL |
|
|
Family ID: |
47594303 |
Appl. No.: |
14/443434 |
Filed: |
November 25, 2013 |
PCT Filed: |
November 25, 2013 |
PCT NO: |
PCT/NL2013/050851 |
371 Date: |
May 18, 2015 |
Current U.S.
Class: |
600/424 ; 356/32;
356/35.5 |
Current CPC
Class: |
H01L 41/16 20130101;
F04C 2270/041 20130101; G01L 1/246 20130101; A61B 2034/2051
20160201; A61B 2034/2061 20160201; G01D 5/35309 20130101; G01L
1/125 20130101; G01D 5/35377 20130101; A61B 5/065 20130101 |
International
Class: |
G01D 5/353 20060101
G01D005/353; G01L 1/24 20060101 G01L001/24; A61B 5/06 20060101
A61B005/06; G01L 1/12 20060101 G01L001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 23, 2012 |
EP |
12194004.3 |
Claims
1. An absolute position measuring device, comprising: an optical
fiber; an optical strain sensor in optical communication with the
optical fiber, and a volume of material deforming under influence
of a magnetic field, wherein the optical strain sensor is arranged
for sensing deformation of the volume of material, and wherein the
device is arranged for multi-dimensional position measurement.
2. A device according to claim 1, wherein the volume of material
deforming under influence of a magnetic field is anisotropic.
3. A device according to claim 1, wherein the volume of material
deforming under influence of a magnetic field is integrated and/or
rigidly connected to a further structure.
4. A device according to claim 1, wherein the optical strain sensor
is arranged for sensing deformation of the volume of material in a
compression mode, a bending mode and/or a torsion mode.
5. A device according to claim 1, wherein the dimensions, material
properties and/or the geometry of the material volume deforming
under influence of a magnetic field are designed such that the
frequency of an external magnetic field falls within a resonance
spectrum of said material volume.
6. A device according to claim 1, wherein the optical strain sensor
includes a fiber bragg grating, a ring resonator, a fiber laser, a
cavity resonator, a Brillouin scattering fiber and/or a Fabry-Perot
interferometer.
7. A device according to claim 1, wherein the optical strain sensor
has a sensitivity axis deviating from the sensitivity axis of the
volume of material deforming under influence of a magnetic
field.
8. A device according to claim 1, wherein the volume of material
deforming under influence of a magnetic field comprises magneto
strictive material, preferably super magneto strictive material,
including material from a group consisting of
Tb.sub.xDy.sub.1-xFe.sub.2, e.sub.81Si.sub.3.5B.sub.13.5C.sub.2,
TbFe.sub.2, DyFe.sub.2 and SmFe.sub.2.
9. A device according to claim 1, wherein the volume of material
deforming under influence of a magnetic field contacts and/or
surrounds the optical strain sensor, preferably such that the
optical strain sensor is embedded in the volume of material
deforming under influence of a magnetic field.
10. A device according to claim 1, further including a sensor
arranged for measuring non-magnetic local physical and/or chemical
quantities, such as pressure, pH, flow, oxygen saturation and/or
temperature.
11. A device according to claim 1, arranged for a minimal invasive
medical application.
12. A method of performing an absolute position measurement,
comprising the steps of: generating a spatially varying magnetic
field; receiving the magnetic field with a device according to
claim 1; interrogating the optical strain sensor, and interrelating
the optical measurement with spatial information of the generated
magnetic field.
13. A method according to claim 12, wherein a time dependent
magnetic field is applied.
14. A method according to claim 13, wherein the amplitude and/or
orientation of the magnetic field is spatially dependent.
15. A method according to claim 12, wherein the magnetic field is
frequency coded.
Description
[0001] The present invention relates to an absolute position
measuring device, comprising an optical fiber, an optical strain
sensor in optical communication with the optical fiber, and a
volume of material deforming under influence of a magnetic field,
wherein the optical strain sensor is arranged for sensing
deformation of the volume of material.
[0002] An increasing number of medical procedures are performed in
a minimally invasive manner, i.e. through small openings in the
human body, instead of using invasive methods, i.e. open surgery.
Advantages of the minimally invasive procedures are a shortened
patient recovery time reducing medical costs, infection risk and
reduced scarring. A main disadvantage is that the surgeon is no
longer able to directly see the object of surgery during the
insertion and the surgical procedure. Therefore, the spatial
localization of medical instruments relative to the tissue of
interest becomes nontrivial, as most instruments bend and twist
during use. Moreover, there is a trend towards steerable and
deformable instruments for minimally invasive surgery and catheter
interventions. This leads to considerable difficulties in a large
number of medical fields.
[0003] Currently, there is a number of ways to deal with the lack
of spatial information on the instruments used in a minimally
invasive surgical environment.
[0004] In a first approach, the inserted instruments are designed
to be extremely rigid. Although this facilitates the spatial
localization of the instrument tip, these instruments cause tissue
damage such as significant bleeding, because they have to be pushed
through overlaying tissue to reach the target location. This
increases the patient recovery time. Also, the application of these
devices is limited, as there are numerous (parts of) organs which
cannot be reached by a straight line from outside the body.
[0005] In a second approach, the inserted instruments are designed
to be more or less flexible and shape sensors are added to the
instrument. An example of such a shape sensor is a sensor optically
measuring a local strain using a set of Fiber Bragg Gratings (FBG).
By nature, these shape measurements are local measurements, and to
obtain the shape of the entire instrument the results of a series
of such shape sensors has to be combined. Therefore, the
error/uncertainty is cumulative, and in practice fairly large.
[0006] In a third approach, inserted instruments are imaged using a
separate imaging method, such as MRI, ultrasound or X-ray. This
offers the advantage of imaging both tissue and instrument. In the
case of MRI, disadvantages include a strongly reduced accessibility
of the patient and limited real-time imaging possibilities. In the
case of ultrasound, a disadvantage is the fact that when applying
the ultrasound transducer manually to the patient, the deduced
spatial location of the instrument is relative to the transducer
instead of absolute. Another disadvantage is that ultrasound images
are highly susceptible to aberrations and artefacts caused by the
tracked instrument itself and by air present in the ultrasound
path. In the case of X-ray, a disadvantage is the fact that when
applying the X-rays both the patient and the medical professional
receive hazardous radiation.
[0007] In a fourth approach, the position of the inserted
instrument is measured based on image guidance using ionizing
radiation (such as CT or angiography). These bulky devices hamper
the clinician during the procedure and use ionizing radiation which
affects the surgeon and patient. Moreover, the position information
is only available during imaging. This means that a high dose is
required or that poor position information of the instrument is
available.
[0008] In a fifth approach, the position of the inserted instrument
is measured using sensors based on a coil and one or more
alternating magnetic fields. Due to induction a current runs
through the coil when a magnetic field is applied. The current is
measured. This approach is in principle quite precise, but the
sensors are fairly large, each coil needs a double wired
connection, and the sensors are susceptible to interference from
electromagnetic sources. The latter is especially problematic
during MRI guided procedures or Radio Frequency ablation
procedures.
[0009] It is an object of the invention to provide an improved
absolute position measurement device to precisely locate medical
instruments, preferably in real-time, for the purpose of minimally
invasive diagnosis and surgery, whilst maintaining minimal
instrument dimensions. Thereto, according to an aspect of the
invention, the device is arranged for multi-dimensional position
measurement.
[0010] By applying optical fiber technology in combination with
material deforming under influence of a magnetic field, the
measuring device can be made extremely small. As an example, the
measuring device can be realized as a structure having a length of
circa 2 mm and a radius of circa 0.01 to circa 0.05 mm which is
considerably smaller than coil based measurement systems. Further,
the measurement device provides in a platform that may easily
include a multiple number of optical strain sensors on a single
optical fiber for performing multiple location measurements, e.g.
for determining the actual shape of the fiber. Due to the limited
dimension of the optical fiber, it is in principle possible to use
two instruments to correlate their mutual position.
[0011] Further, the optical elements and the deforming material in
the measuring device are inherently passive so that no local power
is needed in the fiber, making the measurement device simple, small
and reliable in operation. On the other hand, signal losses in the
optical components are considerably low, thereby providing an
energy efficient measurement device. In addition, the optical
elements and the deforming material are very resistant in view of
interference with electromagnetic external sources such as from MRI
equipment and/or from RF ablation, especially when applying the
deforming material in pre-specified frequency ranges, remote from
the frequency ranges that are applied by other external
electromagnetic sources. A static magnetic field generated in MRI
equipment exerts a force on the volume of material that deforms
under influence of a magnetic field. However, the material volume
can be chosen such that the total force exerted on the material is
low relative to the stiffness of the fiber in its environment.
[0012] The measuring device can e.g. be applied in biopsy needles,
tumor ablation needles, guide wires, catheters and rigid or
flexible endoscopes for real-time measuring a tip position and/or
an overall shape of the flexible instrument.
[0013] The invention also relates to a method of performing an
absolute position measurement.
[0014] Other advantageous embodiments according to the invention
are described in the following claims.
[0015] By way of example only, embodiments of the present invention
will now be described with reference to the accompanying figures in
which
[0016] FIG. 1 shows a schematic view of a first embodiment of an
absolute position measuring device according to the invention;
[0017] FIG. 2 shows a schematic view of a second embodiment of an
absolute position measuring device according to the invention;
[0018] FIG. 3 shows a schematic view of a third embodiment of an
absolute position measuring device according to the invention;
and
[0019] FIG. 4 shows a flow chart of an embodiment of a method
according to the invention.
[0020] The figures are merely schematic views of preferred
embodiments according to the invention. In the figures, the same
reference numbers refer to equal or corresponding parts.
[0021] FIG. 1 shows a schematic view of a first embodiment of an
absolute position measuring device 1 according to the invention.
The device 1 includes an optical fiber 2a-c and an optical strain
sensor 3a,b, e.g. a Fiber Bragg Grating (FBG), a ring resonator, a
cavity resonator, a fiber laser, a Brillouin scattering fiber
and/or a Fabry-Perot interferometer. In the embodiment shown in
FIG. 1, the optical strain sensor is implemented as a FBG. The
optical strain sensor 3a,b is in optical communication with the
optical fibre 2a-c.
[0022] The measuring device 1 also includes a volume of material
4a,b that is able to deform under influence of a magnetic field.
When said volume of material 4a,b is subjected to an external
magnetic field, the dimensions and/or the shape of the volume 4a,b
changes. The optical strain sensor 3a,b is arranged for sensing
said deformation of said volume of material 4a,b. The volume of
material 4a,b contacts the optical strain sensor 3a,b so that the
sensor 3a,b is able to measure a deformation of the volume of
material 4a,b at least in one dimension or direction. In the shown
embodiment, the volume of material 4a,b surrounds a portion of the
optical strain sensor 3a,b. In a specific implementation, the
optical strain sensor 3a,b is inserted in a canal surrounded or
enclosed by said volume of material 4a,b. Alternatively, the
optical strain sensor 3a,b can be mounted on said volume of
material 4a,b, directly or via an intermediate structure. As a
further alternative, the optical strain sensor 3a,b can be embedded
in the volume of material 4a,b. Also, the fiber can be modified,
e.g. by removing a coating to enhance the sensitivity of the
optical strain sensor. The optical strain sensor 3a,b and the
associated volume of material 4a,b deforming under influence of an
external magnetic field constitute a local sensor unit converting a
magnetic field signal via deformation energy to an optical signal.
The optical signal is received via the fiber 2 using an optical
interrogating unit (not shown) that is suitable for optically
communicating with the optical strain sensor 3a,b. Typically, the
interrogating unit generates an interrogation signal that is
converted, by the sensor, into a response signal received by the
interrogating unit. Based on the response signal, a wavelength
shift of the sensor is determined, optionally as a function of
time. The wavelength shift can be related to a deformation of the
sensor.
[0023] In the shown embodiment, the optical fiber 2a-c includes
three optical fiber segments 2a-c interconnected via two optical
strain sensors 3a,b that are aligned with the individual optical
fiber segments 2a-c to form an optical communication chain. The two
optical strain sensors 3a,b are arranged for measuring a
deformation of corresponding volumes of material 4a,b deforming
under influence of a magnetic field. Thus, the device 1 includes
two local sensor units providing local magnetic field information.
It is noted that the device 1 may also include more local sensor
units, e.g. three or five local sensor units, e.g. for determining
an actual orientation profile of the optical fiber 2. Also, the
device 1 may include a single local sensor unit, i.e. a single
optical strain sensor 3 in optical communication with the optical
fiber 2, and a single volume of material 4 deforming under
influence of a magnetic field, wherein the optical strain sensor 3
is arranged for measuring the deformation of the volume of material
4. The device may include a single number or a multiple number of
optical interrogating units. In principle, a single interrogating
unit may communicate with a multiple number of optical strain
sensors, e.g. via a time multiplexing or frequency multiplexing
scheme. When applying a time multiplexing scheme different external
magnetic fields can be generated in a subsequent order. As an
example, mutually orthogonal fields can be generated in a time
sequential order. In this respect it is noted that orthogonal
magnetic fields can be generated by coils having an offset and a
relative orientation with respect to each other. Also parallel
oriented coils may generate orthogonal fields if they are
positioned on a certain distance with respect to each other,
depending on the local spatial orientation of the magnetic flux
generated by the coils. When a frequency multiplexing scheme is
applied different frequency components of the magnetic field can be
generated simultaneously for performing simultaneous measurements.
In this context, the generation of magnetic fields in a frequency
multiplexing scheme is also denoted as frequency coding.
[0024] The volume of material 4 deforming under influence of a
magnetic field may include magneto strictive material such as iron
and nickel. Preferably super magneto strictive material is applied
such as material from a group consisting of
Tb.sub.xDy.sub.1-xFe.sub.2 also called Terfenol,
Fe.sub.81Si.sub.3.5B.sub.13.5C.sub.2, TbFe.sub.2, DyFe.sub.2 and
SmFe.sub.2. The geometry of the volume of material or piece of
material 4 can be such that its dimension parameters are in the
same order, e.g. when the volume is formed as a box or ball.
Otherwise, the geometry may be such that one of its geometry
dimension parameters is relatively small, e.g. when the volume is
formed as a layer. As an example, the volume of material 4 may
cover the optical strain sensor 3 in a circumferential direction.
The thickness of such a cover layer or coating layer may be chosen
such that the deformation of said volume of material caused by the
applied magnetic field has such a range that optical measurement
parameters using the optical strain sensor can be optimized.
[0025] Further, the device 1 is arranged for multi-dimensional
position measurement, e.g. for measurement in a two-dimension or
three-dimensional space, optionally as a function of time.
[0026] During operation of the device 1, the volume of material 4,
e.g. including magneto strictive material, is deformed by an
externally applied magnetic field, and therefore the associated
optical strain sensor is deformed as well. The strain is detected
via the optical fiber 2 using an interrogating unit suitable for
communication with the optical strain sensor. Thus, a local
magnetic field measurement is performed. When information of the
actual spatial magnetic field distribution is available, the
magnetic field measurement can be mapped to an absolute local
position measurement.
[0027] In order to perform a position measurement, the applied
magnetic field is spatially varying so that a relationship between
the amplitude and/or the orientation of the magnetic field versus
the position can be established. Preferably, there is a unique
relation within a space of interest. Alternatively, the
relationship is such that a discrete number of spatial locations
map with a particular amplitude and/or orientation of the magnetic
field, e.g. when applying a spatially periodic magnetic field.
[0028] In principle, the magnetic field can be either static or
dynamic, i.e. time varying. In the case of a static magnetic field,
the orientation of the magneto strictive material with respect to
the magnetic field influences the strain in the sensor providing
information on the orientation and location of the sensor. In the
case of a dynamic magnetic field, the magnetic field may be varying
by magnitude and/or orientation. As the magnitude and the
orientation of the applied magnetic field is known, the measured
strain at the sensor can be correlated to this field and the
position and orientation of the sensor (up to 6 degrees-of-freedom)
can be calculated. Also, a combination or a static field and a
dynamic field is applicable, e.g. by generating a first, static
field having a behaviour dependent on a first spatial dimension,
and a second, dynamic field having a behaviour dependent on a
second and third spatial dimension.
[0029] In the embodiment shown in FIG. 1, a first and a second
magnetic field generating unit 10, 11 generate a first and a second
magnetic field B.sub.1 and B.sub.2, respectively. In principle,
also a single magnetic field generating unit can be applied, or
more than two magnetic field generating units, e.g. 3 or 6 magnetic
field generating units. The magnetic field generating units can be
positioned static, or their position and/or orientation may change
over time to generate another magnetic field. The units 10, 11 may
include coils generating magnetic fields. Alternatively, other
magnetic field generating devices are applied e.g. an
electromagnet. Further, multiple groups of magnetic field
generating devices can be applied for providing a magnetic field
having a desired profile in space and/or time. Generally, the
generated magnetic field is a vector field having an orientation
and amplitude. When the magnetic field is varied in at least three,
preferably orthogonal, directions, the multi-dimensional location
of the optical strain sensor 3 can be determined by triangulation.
It is also possible to vary the magnetic field in two or one
direction(s) and then measure the magnetic field using two or more,
preferably orthogonal oriented, local sensor units. For example,
the magnetic field may vary in two orthogonal directions while two
or more orthogonal local sensor units are used at the measurement
location. Generally, when increasing the number of magnetic fields,
less local sensor units are required to obtain position and/or
orientation information. On the other hand, when increasing the
number of local sensor units, less magnetic fields are required to
obtain the position and/or orientation information. Preferably, the
number of local sensor units is small to minimize invasive
intervention. The desired information about position and/or
orientation can be obtained by interrogating the limited number of
local sensor unit with multiple magnetic fields.
[0030] By using a single or a multiple number of local sensor units
at a particular part of the fiber, the multi-dimensional position
of a particular part of the fiber 2 can be determined. Further,
when applying further local sensor units, at other fiber parts, an
actual shape of the fiber can be derived, so that not only the
local position but also the local orientation of the fiber can be
measured.
[0031] Advantageously, a background natural and/or synthetic
magnetic field is measured and compensated before an actual
position measurement starts, thereby rendering the measurement more
accurate. Further, any natural and/or synthetic magnetic field
might be used for performing the position measurement. As an
example, the earth magnetic field might be used as the external
magnetic field influencing the local sensor units. As a further
example, the field generated by another apparatus can be used for
performing the location measurement, such as a MRI scanner, an
electron microscope or a containment field of a fusion reactor.
[0032] In a specific embodiment, the dimensions, material
properties and/or geometry of the material volume deforming under
influence of a magnetic field are designed such that the frequency
of an external magnetic field falls within a resonance spectrum of
said material volume, thus rendering the local sensor unit more
sensitive with respect to the magnetic field. More specifically,
the geometry of said material volume can be designed such that
specific resonance spectra can be set in mutually different
directions. As an example, a material volume in a length direction
may have a first resonance spectrum, in a width direction a second
resonance spectrum, and in a depth direction a third resonance
spectrum. Such a design enables a simultaneous measurement in three
orthogonal directions using a single optical strain sensor and an
external magnetic field having three selected frequencies, and
interrogating the optical strain sensor on a frequency division
basis.
[0033] FIG. 2 shows a schematic view of a second embodiment of an
absolute position measuring device 1 according to the invention.
Here, the three optical strain sensors 3a-c are implemented as
(optical) ring resonators oriented in mutually orthogonal
directions. The ring resonators are embedded in volumes of material
4a-c, e.g. magneto strictive material, deforming under influence of
a magnetic field. The three ring resonators 3a-c associated with
the magneto strictive material form three separate local sensor
units. It is noted that, in principle, the mutual orientation of
the ring resonators 3a-c can be arranged in another way, e.g. in a
tilted orientation. Further, an optic cavity can be formed having
different sizes in different dimensions. Also, three separate
sensors can be arranged in series while the fiber carrying the
sensor has a local different orientation so that the sensors are
also mutually oriented differently. It is noted that the ring
resonators shown in FIG. 2 can be implemented as other optic strain
sensors.
[0034] FIG. 3 shows a schematic view of a third embodiment of an
absolute position measuring device 1 according to the invention.
Here, two or three ring resonators 3a,b are embedded in a single
volume of material 4 deforming under influence of a magnetic field.
The ring resonators are thus integrated in a single local sensor
unit providing multiple-dimensional location information. In
alternative embodiments, even more than two ring resonators are
embedded in a single volume of material 4 deforming under influence
of a magnetic field, e.g. three ring resonators. Again, the mutual
orientation of the ring resonators can be selected, e.g. as a
mutually orthogonal orientation.
[0035] In a particular embodiment, the sensitivity axis of a
direction dependent optical strain sensor, e.g. an FBG or a ring
resonator, differs from a sensitivity axis of the volume of
material 4 deforming under influence of a magnetic field. Then, the
sensitivity axis of the optical strain sensor deviates from the
volume of material sensitivity axis, e.g. by exploiting any
anisotropic properties of the material 4 deforming under influence
of a magnetic field. Especially, magneto strictive material can be
applied that deforms under influence of a magnetic field in an
anisotropic manner. Generally, the sensitivity axis of the volume
of magneto strictive material 4 or other volume of material
deforming under influence of a magnetic field may coincide or
deviate from the axis of the associated optical strain sensor. In a
specific embodiment, the magneto strictive material sensitivity
axis is transverse relative to the optical strain sensor axis. It
is noted that the shape of a ring resonator can be designed such
that it is most sensitive to strain in a pre-specified direction.
Similarly, the sensitivity axis of the volume of magneto strictive
material 4 may differ from the orientation of the optical fiber
2.
[0036] Advantageously, a coil is wrapped around the volume of
material 4 deforming under influence of a magnetic field, to make
the magnetic field sensed by the material more uniform and
directional, and thus to optimize the sensitivity of the
sensor.
[0037] In an embodiment, the volume of material deforming under
influence of a magnetic field is integrated and/or rigidly
connected to a further structure. As an example, the further
structure is a substance wherein the volume of deforming material
is integrated, such as an epoxy matrix. In a first implementation
the volume of deforming material includes elongate elements
embedded in the integrating substance, forming a 1-3 composite
structure. In a second implementation the volume of deforming
material includes ball shaped elements embedded in the integrating
substance, forming a 0-3 composite. The ball shaped elements can be
arranged in interrupted line segments. In a third implementation
the volume of deforming material and the integrating substance form
a sandwich structure with a single or a multiple number of laminar
layers. As a further example, the deforming material is rigidly
connected to a further structure such as a metal plate.
[0038] By integrating and/or rigidly connecting the volume of
deforming material to a further structure, the resonance frequency
of the combined structure, forming a multi material structure, can
be modified. As an example, the resonance frequency of the combined
structure is higher or lower than the resonance frequency of the
volume of deforming material itself, thereby rendering the
measuring device suitable for performing sensitive and accurate
measurements in a frequency regime that falls outside the intrinsic
resonance spectrum of the deforming material volume. Further, by
integrating and/or rigidly connecting the volume of deforming
material to a further structure, any anisotropic deforming behavior
of the deforming material can be enlarged or reduced.
[0039] Further, the optical strain sensor can be arranged for
sensing deformation of the volume of material in a compression mode
or in another mode, such as a bending mode and/or a torsion mode,
thereby providing further design options to operate the measuring
device in a desired resonance frequency regime.
[0040] It is noted that during operation of the device, the volume
of material deforming under influence of a magnetic field deforms,
i.e. the volume shape and/or volume dimensions of the material
modify as a function of time. The volume of material deforming
under influence of a magnetic field forms a body deforming when an
external magnetic field is applied. The deformation can be either
isovolumetric or non-isovolumetric. In the first case, the total
content of the material volume or body remains constant. In the
latter case, not only the shape and/or dimensions of the material
volume or body vary, but also the total volume content changes in
the deformation process. In a medical setting, the measuring device
can be integrated with a minimally invasive surgery unit, so as to
determine the local position and/or orientation of the surgery
unit. Advantageously, the measuring device includes a single or a
multiple number of further sensors arranged for measuring
non-magnetic local physical and/or chemical quantities, such as
pressure, pH, flow, oxygen saturation and/or temperature. Then, a
time-continuous spatial localization of (medical) instruments in a
complex and high interference environment is combined with further
measurements while the increase of device dimensions can be
minimal.
[0041] FIG. 4 shows a flow chart of an embodiment of the method
according to the invention. The method performs an absolute
position measurement. The method comprises a step of generating 110
a spatially varying magnetic field, a step of receiving 120 the
magnetic field with a device according to claim 1, a step of
interrogating 130 the optical strain sensor, and
a step of interrelating 140 the optical measurement with spatial
information of the generated magnetic field.
[0042] The above described measuring device can advantageously be
used in a medical context, in particular meeting the need for a
method to precisely locate medical instruments in real-time for
minimally invasive diagnosis, catheter interventions and surgery,
whilst maintaining minimal instrument dimensions. This is relevant
for a large number of medical fields.
[0043] As a first example, the device can be used in a so-called
radiofrequency (RF) or cryoablation of tumors for oncological
treatment of patients. In this procedure, a needle mounted on a
catheter is inserted into the tumor, which is then either heated
(RF ablation) or cooled (cryoablation) to treat (kill) the tumor
tissue. Often, the needle needs to be inserted multiple times to
treat the entire tumor. Moreover, multiple tumors are frequently
treated in a single procedure. Although the procedure is usually
performed under guidance of an imaging modality such as ultrasound,
MRI or CT, these modalities either suffer from artefacts produced
by the needle itself or do not provide real-time measurements. This
means that--when using such imaging modalities--there is a large
uncertainty in the placement of the needle itself, leading to a
considerable risk that parts of the tumor are not ablated.
[0044] As a second example, it is noted that similar problems occur
during the taking of needle biopsies, where punctures at erroneous
locations occur often (e.g. in 20% of breast biopsies), or during
brachytherapy, where radioactive markers are placed inside or near
a tumor. In the latter case the so-called snaking of the placement
catheter leads to uncertainty on the marker location and thus to
suboptimal treatment.
[0045] As a third example, it is noted that ablation therapy is
also applied to treat cardiovascular diseases, such as atrial
fibrillation. Here, there is also considerable uncertainty in the
placement of the ablation catheter relative to the heart and
imaging modality leading to significantly increased treatment times
and to unintended removal of cardiac tissue. The above described
measuring device can advantageously be used for accurately placing
the ablation catheter.
[0046] As a fourth example, the sensor can be applied for placing a
guide wire and monitoring that the guide wire remains in a desired
position/orientation. Further, the sensor can be applied to monitor
that a surgical instrument guided by the guide wire is moved to a
desired location, e.g. near a marker on the guide wire.
[0047] As a fifth example, there are considerable difficulties in
the fusion of datasets produced by non-invasive imaging techniques,
e.g. ultrasound, MRI, CT, SPECT or PET, and catheter/endoscope
based imaging methods, because of the limited precision of
non-invasive imaging techniques and imaging artefacts induced by
the catheters and endoscopes used.
[0048] The above described measuring device can advantageously be
used in these contexts, thus leading to improved diagnoses in
medical fields, increasing the efficiency of medical treatment,
improving patient quality of life, increasing patient life
expectancy and reducing healthcare costs.
[0049] It is noted that the absolute position measuring device
according to the invention can not only be applied in the medical
fields of minimally invasive diagnostics and surgery, but also in
other fields, such as e.g. electron beam localization, electron
microscopy or electron imaging.
[0050] The invention is not restricted to the embodiments described
herein. It will be understood that many variants are possible.
[0051] As an example, the local sensor unit may be located at an
end section of the fiber. However, the local sensor unit may also
be located at an intermediate part of the fiber.
[0052] Other such variants will be apparent for the person skilled
in the art and are considered to fall within the scope of the
invention as defined in the following claims.
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